How To Fit A Bearing On A Shaft Or A Bore?

martik777 said:

You could advance with your compound (instead of the cross-feed) set at various angles to reduce the amount taken off, for example, at 5.7° .001 on the compound will move the tool bit in .0001

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+1 on a great old idea.

Just make sure that it is set at 5.7 deg. to the spindle and not to the ways. i.e., if your compound reads 0 deg. when the compound advances parallel to the cross feed, set at 84.3 deg.; if it reads 90 deg., set at 5.7 deg.

Bob

When using the heat and cold method of mounting a bearing on a shaft you HEAT THE BEARING and COOL THE SHAFT. I do this all the time mounting bearings on crank shafts in Model Engine Repair. I have a toaster oven for the bearing and a small freezer for crank shafts.

"Billy G"

I remember our shop made steel wheels with brass tires. Those who put them together would freeze the wheels and heat the tires causing a hard press fit when they cooled. I remember grinding the pressed parts flat on a surface grinder. Then someone else probably stacked them together and took a skim cut to make all of them perpendicular. We must have made 100s over the years. The were used in seam welders to weld appliance cabinets.

prasad said:

Guys

I am running into difficulty while trying to fit ball bearings. The bearing I have is about 5.5" in diameter.
I want the bearing to stay in its place once mounted on the shaft or bore but I always end up with it sliding away. As I get close to the desired diameter I reduce the cut to bare minimum steps. The shaft is still not accepting the bearing. So I take one more tiny cut using the same depth setting on my cross slide dial with a hope that it will give me the required diameter. Then I find the shaft is too loose for the bearing. I have the same exact experience in boring too. I dont know how else to do it. One moment it appears too tight and next time it is too loose. When am I going wrong? What is the right method to get it right? I do not want to use loctite to get over the loose sliding fit.

Thanks
Prasad

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Generally bearings are fitted with either the shaft or the housing an interference fit. The most common approach is if the shaft is rotating then the that will be the interference fit, and generally 0.001 per inch of dia.

The housing should be a firm sliding fit, and the bearing held in place with a circlip or a plate held on by screws. leaving a small end float clearance, at least on one end of the shaft. to allow for thermal expansion, sometimes a spring might be used to keep it loaded in one direction.

In the case where the housing is rotating then the interference fit should be between the outer race and the housing, otherwise it's the same procedure.

When fitting an interference fit bearing onto a shaft, do NOT bash it on, the preferred method is to heat bearing in good machine oil to about 70c or 160f if the bearing has rubber seals consult bearing supplier for max temperature. You may also cool the shaft if possible.

If heating is not possible you can press it on, with a driving sleeve on the inner race only, also use plenty of good machine oil on the shaft to prevent scoring. If you have no alternative but a hammer make up a sleeve to fit over the shaft and drive on the inner race only.

When fitting to a housing the same principals apply except you must only apply pressure to the outer race. Never apply axial pressure to a ball race that will be transferred though the balls.

I worked machine repair rebuilding high speed spindles, and always used a heat lamp to heat up the bearings to drop on the shaft.

bobshobby said:

In the case where the housing is rotating then the interference fit should be between the outer race and the housing, otherwise it's the same procedure.

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Can you explain why you want to do this? I thought it would be the same as with a shaft moving because the bearing would expand from the heat and tighten itself up in the housing.

Thank you.

bobshobby said:

In the case where the housing is rotating then the interference fit should be between the outer race and the housing, otherwise it's the same procedure.

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Can you explain why you want to do this? I thought it would be the same as with a shaft moving because the bearing would expand from the heat and tighten itself up in the housing.

Thank you.

Hellkell said:

Can you explain why you want to do this? I thought it would be the same as with a shaft moving because the bearing would expand from the heat and tighten itself up in the housing.

Thank you.

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It is common engineering practice, I thought I had explained it, what bit do you not understand?

Kernbigo said:

I worked machine repair rebuilding high speed spindles, and always used a heat lamp to heat up the bearings to drop on the shaft.

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Yes that will work, any process that gives a gentle even heat is ok. Do NOT use an oxy torch. Some people put them in an oven and set the thermostat, that is ok.

As a marine engineer where we wanted maximum service life under extreme conditions we always kept a tank of light machine oil fitted with an electric element and thermostat, bearings were put in the tank when we started pulling a machine down so they were ready to simply drop on at the right time.

Most of the time when that machine was due for an overhaul after five years, the bearings were still fine, but we always replaced them anyway. Bearings are cheap compared to a breakdown and the labor to replace them.

Sometimes the replacement bearings for very special highly rated equipment would come in a sealed tin that was already full of the oil; that they would run in, much like a large jam tin, special heating instructions were printed on the label. You've gotta believe it, if they weren't followed, then premature failure was very high on the cards.

bobshobby said:

It is common engineering practice, I thought I had explained it, what bit do you not understand?

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Maybe you're misunderstanding my question. I was talking about the bearing in use heating up and expanding not heating it in oil to install it.

I am wondering why in both cases you wouldn't have a tight fit on the shaft so as the bearing heated up from use it would expand and tighten up inside the housing. Seems no different to me whichever race is moving or stationary.

Just wondering the theory behind it. Thank you.